Actually maybe Tentacool deserves a boost to High too. You can catch it at a high level (ranges from 5-40 by Surfing) and it evolves into Tentacruel at level 30 (you can also fish up a Tentacruel in Yellow). Tentacool has 100 Special and 70 Speed, and then gains 120 Special and 100 Speed after evolution. It can run a set of Surf, Ice Beam/Blizzard and Mega Drain for coverage (Mega Drain is weak but helps it beat opposing Water types which is something some other Water types struggle with). Sounds pretty cool.

Then again, I guess the Psychic and Ground weaknesses aren't helpful...

^Yeah, but there are barely any pokes who use Psychic / Ground outside of Sabrina (and Giovanni, but Tentacruel will one-shot everything with a Ground attack). Yeah, if you can get a level 35-40 Tentacool, it sounds like it could be rididulous late game-- 120 Special is stupid good. Dewgong and co. can't touch Tenta's resistances and 120 Special, so Mega Drain sounds like it would be nutz.

Super Moderator

In RB, the only Ground move Giovanni has that hits you for SE is Dugtrio's Dig, which you could just switch out of. In Yellow he put it on every Ground-type he has though.

Mega Drain PP will not be an issue until like Victory Road. And if you run out of PP you'll just have to use something else on your team to deal with Waters, like whatever you gave Thunderbolt to. Not a big problem.

I'm not surprised that the higher level ones are rarer, but assuming that you'd want to get one at at least level 30, 6 encounters in 20 minutes isn't that bad, and of course Repels will help you find it sooner if you have a pokemon at the appropriate level to lead with.

Also, the minumum level of Tentacool in Seafoam Islands is 20 rather than 5. It might be better to try there. Plus there's also fishing (this is only worth it in Yellow I think).

EDIT: Actually Tentacool is only found in the Seafoam islands in Yellow.

So yeah I definitely think it deserves at least High. As I said, good power (I think it has the most powerful Surf in the game) and movepool, comes at the right time, and can be obtained at a reasonable level.

Right so I don't have enough time to do another playthrough of Yellow to test Psyduck/Golduck, but I don't think a testrun of Yellow would tell us much anyway. Some of the gym leaders are a bit harder on Golduck, but other than that Golduck arrives at the same time and is likely to face the same things in either version. Therefore, the only thing we need to consider is if the level difference is enough to cause a tier drop.

Therefore, I decided to time how long it would take to obtain a Golduck from the pond north of Vermillion City and train it to match your team.

It took me about 10 minutes to find a Golduck. 5% encounter rate (on a patch of water where the chance of encountering a pokemon is low) is a bit irritating. Unfortunately, the Golduck was level 15 rather than level 20, but I decided to use that one instead of searching for longer.

After that, I taught it Surf and I grinded to level 33 (this wasn't what I originally intended to do but I didn't think going any longer than that would help me in any way so whatever). It took about 1 hour and 10 minutes! First I started grinding in Rock Tunnel for some initial experience (Diglett's Cave would be ok too, but I think Rock Tunnel is safer). Once I got to about level 24, I went over to Cycling Road where Ponyta gives an easy 600+ experience per kill. Surf was a 2HKO on Fearow, who gives a similar amount, and Doduo gives 300+ and is easy to kill too. If you have Ice Beam (which I didn't because I was using the same save file as my last playthrough) then it's even better because more PP means less trips to the pokemon centre. The last few levels went by quickly for me.

Also, as I said my Golduck was level 15. If you get one at level 20 then you can probably save about 20 minutes of grinding.

Not sure if using Psyduck instead would have been better. You save time not looking for Golduck (which is 10 minutes for me) but it might be a bit harder to grind on Cycling Road (I reckon Fearow would be harder to take down with Psyduck).

Take all of this as you will. I think that if RB Golduck is going into High, then Yellow Golduck should be at least Mid. However, it might just be easier and less time consuming to keep them together rather than separate them...

I just noticed the Gyarados entry is wrong about her matchup against Agatha, at least in that it gets no super effective moves for her. Gyarados technically has access to Earthquake (if you want to use THAT TM on it). Earthquake + Ice Beam / Thunderbolt would give Gyarados an easy sweep against her, hitting every one of her Pokemon for a massively powerful super effective hit. Pretty sure that at a sufficient level it could OHKO all of them.

I've used Gyarados against Agatha before and it does pretty well (her ghosts don't know Thunderbolt), just gotta watch out for Confusion hax. But you are better off just using something that can spam Earthquake/Psychic.

Am I the only one who thinks something's wrong with Seel being in Top tier? It's slow, misses quite a bit more than a half of the game and needs the Ice Beam TM to be useful against the key trainers lategame. The analysis mentions natural access to Ice Beam, but it's not until L56 that you get it, which is out of reach regardless of whether it gets boosted experience or not. I also fail to see how it solos the game (which the analysis claims it to do); for example, how is it taking on Hitmonlee when he's faster and has Hi Jump Kick? Its special attack is nothing spectacular to expect a OHKO against Machamp either. Don't quite understand how it's beating Venusaur either (Razor Leaf is present on the set). Also, if Venusaur is on rival's team, doesn't that mean you started with Squirtle but chose to not use it?

Dewgong's not even that good against Blaine, since Fire Spin prevents it from moving (and it's slower than Blaine's speedy Pokemon) and fire-type moves hit it for neutral damage (no Thick Fat either).

Dewgong isn't slow. 70 Speed isn't slow in RBY. It is only getting outsped by extremely fast opponents. You will be going first the majority of the time. Low Speed is only an issue if it is really bad, like Slowbro and Snorlax.

It doesn't need the Ice Beam TM because it gets Aurora Beam straight away which gets the job done. If you are using Aurora Beam then you rely on Surf as your main move and you use Aurora Beam when it is super effective. Trust me, it works fine. Furthermore, there are 2 Ice TMs, and it is very unlikely that you would have used both of them already in a normal playthrough. Typically, if you are using a water type, it is standard to reserve one of them for the water type on the team.

The analysis doesn't claim Dewgong can solo the game.

I outsped Hitmonlee and killed it with Surf. I did actually OHKO Machamp with Surf because the extra experience made me rather overlevelled, although the analysis doesn't even say that it can anyway.

The Venusaur mention was probably inappropriate, although it technically doesn't claim to beat it 100% of the time. It just says that its STAB covers it. It is just making the point that if you need to hit Venusaur hard (e.g. to finish it off) then Dewgong is capable of doing that. You are right in saying that Venusaur being on the team means that you picked Squirtle, but I don't see how that is relevent. It isn't up to us to decide what the player uses. That's not to mention that it is perfectly possible to use both Squirtle and Seel on the same team if you want to.

Eevee (Flareon) - Mid Tier
-Availability: Flareon is given to you as a level 25 Eevee, and can be evolved via a Fire Stone, which costs an easily affordable 2100 Poke.
-Stats: Flareon not only posesses high attacking stats on both ends of the spectrum, but it also has enough speed to outpace anything that isn't particularly fast or is used by a Gym Leader/Elite Four member. Its Defense and HP do let it down, though.
-Movepool: Flareon starts off with Tackle (Quick Attack in Yellow) as its most powerful move, which makes Body Slam an option to be considered. However, Flareon learns an adequate move a few levels after obtaining it (Bite at level 30 in Yellow and Ember at level 31 in Red and Blue), but Body Slam should still be at least considered, as its extra base power nets it OHKOes where Bite and Ember do not. Of course, being a Fire-type, Flareon has TM access to Fire Blast, and considering the fact that all Flareon learns in terms of attacks are either Fire-type or Normal-type moves (unless you're actually counting the pathetic Smog as a usable attack), Flareon will easily have space for it. Also, Flareon learns Fire Spin at level 42 (level 36 in Yellow), but while Fire Spin's trapping effect might seem appealing at first glance, it slows the game's progress immensly, making it not recommended.
-Power: As mentioned above, before it learns Ember/Bite (and also assuming that you didn't teach it Body Slam), it has a noticable lack of power and as such has trouble early on when you first get it. Once it learns Ember/Bite, its combat abilities improve considerably, but its low combined Defense and HP cause its health to wear down quickly, and more often than not, it generally ends up being the first Pokemon in your party to faint. When the water routes come along, Flareon predictably has a bit of a rough time, but its incredible Attack allows it to fend for itself better than an Arcanine or Ninetales would. Also, teaching it Body Slam helps it out greatly, allowing it to achieve multiple OHKOes that Bite and Ember can't.
-Type: Fire typing, while helpful in Celadon and against the random Grass-type user, doesn't really stand out anywhere else, and causes it to have trouble late-game, where Water-types are abundant.
-Match-ups:
--Erika: Her Victreebel happens to be faster than you and knows Wrap. Thankfully, her Tangela and Vileplume happen to be slower than you and thanks to RBY's AI, they will never use Mega Drain or Petal Dance against you, as it would be not very effective, thus allowing Flareon to Bite (or better yet, Ember) its way through her team.
--Koga: Let's face it. While Ember's power is enough to cut it against the average trainer, it's just not enough to so much as 3HKO his Muk or Weezing. Things might seem better in Yellow at first glance, with his entire team being weak to Fire-type attacks and weak overall, but the problem is that Flareon's only Fire-type attack at that point in the game is Fire Spin, which burns time more efficiently than Koga's multiple Venonat.
--Sabrina: By this time, Flareon should be high enough in level that it can withstand 2 Psybeams from her Pokemon, and Bite should be doing more to Kadabra than Recover heals. Flareon can also beat Alakazam if it knows Body Slam, but only if it paralyzes it. In Yellow, however, Flareon would need to be lucky to beat her Kadabra by itself, and this is assuming it knows Body Slam!
--Blaine: Thanks to RBY's AI as mentioned above, Blaine's Pokemon will never use a single Fire-type attack against Flareon. It still has to watch out for Rapidash's Stomp and Arcanine's Take Down, with the former being faster than Flareon, thus giving Stomp the chance at flinching Flareon, and the latter coming off of a respectable Attack stat. Still, Flareon should be able to beat every Pokemon on his team, with the possible exception of Arcanine, with little worry.
--Giovanni: Flareon can't do much to Rhyhorn or Rhydon without wasting Fire Blast's PP, which isn't enough to deal with both of them. Also, every one of Giovanni's Pokemon (except Persian) threatens Flareon in Yellow, thanks all of them knowing Earthquake, but regardless of version, Flareon flat out loses to Dugtrio. Thankfully, the Nidos are manageable in Red and Blue.
--Lorelei: Simply put, the only Pokemon of hers you should even consider having Flareon fight is Jynx. It falls on its face against anybody else.
--Bruno: The 2 Onix he has aren't worth wasting Fire Blast's PP. Let somebody else deal with them. Fire Blast OHKOes both of the Hitmons, but Machamp can stomach a blast. Keep in mind though that his Hitmons are faster than Flareon.
--Agatha: Flareon can't do much to her Ghosts, thanks to their having a Special that is enough to take minor damage from even Fire Blast combined with an immunity to Normal-type attacks. Her Golbat and Arbok are both faster than Flareon and can withstand a Fire Blast, but outside of status, Golbat (and Arbok in Red and Blue) won't be doing much back.
--Lance: Flareon won't be doing much of anything this fight, as all of them not only resist Fire Blast, Flareon's main attack, but they all know Hyper Beam, which does a large amount of damage to whatever doesn't resist it or have respectable Defense, and simply put, Flareon does not fit either of the above criteria.
--Rival: Pidgeot, Exeggutor, and Venusaur are all easily beaten. Flareon can potentially beat Alakazam, but it needs Body Slam and don't expect it to do much else, as Psychic can easily wear it down, and the same goes with Jolteon. Also, unless you're using it as fodder (which I hope you're not), Flareon should never go up against Gyarados, Cloyster, or Blastoise, for obvious reasons.
-Additional comments: While Flareon isn't much of a help against the game's major battles, its performance against the trainers after Pokemon Tower (as well as doing better against Water-types than its non-Charmander competition) makes up for it, and makes Flareon an acceptable choice for a spot on your team.

So there's the first of the revamps. Expect to see the next one (Slowpoke) some time tomorrow, and in the meantime, thoughts and criticisms about the Flareon revamp are appreciated (but not necessary).